The disappearance of Malaysia Airlines Flight 370 has left experts perplexed, leading to a variety of unsubstantiated theories about what might have happened. Unfortunately, if history is any judge, it's possible we may never know. Here are five other examples of missing flights that vanished without a trace, and remain unsolved to this day.

Amelia Earhart

Perhaps the most famous missing pilot in history, Amelia Earhart vanished over the central Pacific Ocean near Howland Island in 1937 during an attempt to become the first female to circumnavigate the globe by flight. Though some clues have emerged over the years, and theories abound, Earhart's plane has yet to be found.

A recent discovery off the coast of Nikumaroro island, an uninhabited tropical atoll in the southwestern Pacific, offers new hope that the Earhart mystery may soon have a resolution. A sonar scan has revealed what some experts believe could be Earhart's crashed Lockheed Electra plane, and an expedition to the island is scheduled in 2014 to look into the findings. Lending credence to the evidence, researchers have previously found what appears to be a jar of '30s-era freckle cream on Nikumaroro island, along with an American-made woman's compact, buttons and the zipper from a flight jacket.

Could this be Earhart's final resting place? We'll have to wait for the expedition to know for sure.

Flight 19

Flight 19 consisted of a fleet of five TBM Avenger torpedo bombers that disappeared over the Bermuda Triangle on Dec. 5, 1945, during a routine training mission. The fact that all five of the planes and all 14 of the airmen on board vanished without a trace has fueled the myth of the Bermuda Triangle. No wreckage from any of the planes has ever been found, though an investigation involving the recorded radio transmissions from the planes has determined that navigational errors likely drew the planes off course into the Atlantic Ocean, where they ran out of fuel and crashed.

Stolen Boeing 727-223 Angola Plane

Here's an intriguing aviation mystery for you. On May 25, 2003, a decommissioned Boeing 727-223 plane mysteriously began taxiing down a runway at the Quatro de Fevereiro Airport in Luanda, Angola. It took off without clearance, and disappeared into the sky, never to be seen or heard from again. It is believed that at least one man was on the plane at the time of its departure: Ben Charles Padilla, an aviation engineer and pilot. His motive for stealing the plane, if indeed he intended to steal it, remains a mystery. No trace of the plane or Padilla have ever been found.

Star Tiger & Star Ariel

Two separate flights of Avro Tudor planes that went missing in the Bermuda Triangle have added fuel to the fire about the mythology of that region. The Star Tiger disappeared over the Atlantic Ocean while on a flight between Santa Maria in the Azores and Bermuda on Jan. 30, 1948. The flight experienced extreme weather and winds during the flight, so investigators assume the plane was blown off course and ran out of fuel, or was forced to crash land in the choppy waters.

The Star Ariel's disappearance was far more mysterious, however. It took off in excellent weather conditions on Jan. 17, 1949, on a flight between Bermuda and Kingston, Jamaica. The last radio transmission from the flight reported good visibility and smooth flying, but the plane was never heard from or seen again. The entire fleet of Tudor IV's was retired after both the Star Tiger and Star Ariel were lost within the span of 12 months.

Flying Tiger Line Flight 739

Flying Tiger Line Flight 739 was a Lockheed L-1049 Super Constellation propliner chartered by the U.S. military in 1962 to fly 96 American soldiers from Travis Air Force Base in California to Saigon, Vietnam. The flight landed in Guam for a scheduled refueling and departed without incident for its next stop in the Philippines. About 80 minutes into that leg of the flight, the pilot radioed a routine message and reported no trouble, but that was the last contact the plane ever had.

The search for the plane was, at the time, one of the largest to ever take place in the Pacific, covering more than 200,000 square miles of ocean, but the aircraft was never seen or heard from again.